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Date: Mon, 10 Mar 2014 10:58:45 -0700
From: "H. Peter Anvin" <hpa@linux.intel.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Stefani Seibold <stefani@seibold.net>,
        Andreas Brief <Andreas.Brief@rohde-schwarz.com>,
        Martin Runge <Martin.Runge@rohde-schwarz.com>
Subject: Re: [x86, vdso] BUG: unable to handle kernel paging request at d34bd000
References: <20140307013833.GD8427@localhost> <1394176888.1018.3.camel@wall-e.seibold.net> <CALCETrVCwZWvd78urw+O4zD3PoNZTQxg8FMzTrUi4+5w9rC5=A@mail.gmail.com> <1394229220.20013.13.camel@wall-e.seibold.net> <CALCETrXB0G3aA1Usp4U-9-eN0z22YC4Sn+3z42mrU2ab0gE9gQ@mail.gmail.com> <1394354848.1002.37.camel@wall-e.seibold.net> <531D044C.2090303@linux.intel.com> <CALCETrXJobOnVB-ne9s57o3Z1KwK4fRtaYi8W=L4+UT065fKJw@mail.gmail.com> <CALCETrUyJWQnQsX22+wrvPbXkj67nhZ0SMP1_hCo2yZ+Z5tMyA@mail.gmail.com> <531DD35A.5060202@linux.intel.com> <CA+55aFwKpBybz9S9A=+tcr1BbdzAbagL30Br2cak2GrdPH=hhA@mail.gmail.com> <CALCETrW6CT2ceHiHzMaZUGkwEBFWQEemFS5Fj=V7Wg-cNArMLg@mail.gmail.com> <531DF549.2090403@linux.intel.com> <CALCETrV+3yCfOCJzRKN-woOyp2RF_=dW1V=9CwpYTUNGAiLoNQ@mail.gmail.com> <531DF896.8010305@linux.intel.com> <CALCETrVKfBpVHZcyccWRYM4rdOAETSQsxjiQuxn+0AeX78XiEw@mail.gmail.com> <531DFAF0.9070806@linux.intel.com> <CALCETrVkTtt5H9-0_mODcGyaLTusBfANkoANo+wKB4JAwjxU2g@mail.gmail.com>
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On 03/10/2014 10:52 AM, Andy Lutomirski wrote:
>>
>> Hint: where is your RIP?  Where is the RIP of other processes?
>>
> 
> Whoa there, I'm not suggesting anything nearly that crazy :)
> 
> I'm suggesting changing out the vvar page *for that process*, which is
> not executable.  The actual vdso code already supports this -- from
> userspace's point of view it's the same thing as 'echo acpi_pm >
> /sys/devices/system/clocksource/clocksource0/current_clocksource',
> except that if the actual clocksource is HPET, the hpet page will be
> switched out (presumably with a zero page) while being read.
> 
> Other processes are totally irrelevant, unless they share the same
> struct mm.  (This is why the vvar page can't be in the fixmap for this
> to work.)
> 

I meant "threads" not "processes"...

	-hpa